Saturday, 28 May 2016

real analysis - A necessary condition to $F'(x)=f(x)$ for a continuous function $f$


Theorem: Consider ,



$$F(x)=\int_a^xf(t)\,dt$$



If the function $f:[a,b]\to \mathbb R$ is continuous then , $F(x)$ is differentiable and $F'(x)=f(x).$




I know that the continuity condition of $f$ is sufficient condition.




That means there exists a discontinuous function $f$ for which this $F'(x)=f(x)$.



My Question:



Does there exist a necessary condition for this ?



$$OR$$



After imposing which extra condition on $f$ it is necessary that $F'(x)=f(x)$ ?

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